[help][advice] C++ program evaluation and feedback

My name is Jay and I started to learning programming about a year ago, I am studying computer science at university and I learned some C and Java from uni, but I've also learned C++ recently from Bucky's youtube channel, and I want to say thank you to Bucky, you've taught me things that I haven't yet learnt from university!

Recently I've made this little program in C++, it encrypts messages based-on the vigenere cipher technique, users can input both the message and the key as they wish. I would like to post it here and ask if anyone could take a look, give me some feedback, because I'm still new to C++, and it'll be very helpful for me to improve my programming skills.